Eddie George was the first NTSC cover player, and he had a career high in carries, yards, TDs (Rushing and Total), and his team won their division grabbing the #1 seed. The only thing that could possibly be considered a "curse" would be the fact that they lost in the Divisional round (to the eventual SB champ, considered to have one of the best Defenses of all time).
Ray Lewis, had a less than stellar season by his standards, but still an excellent season overall.
Vince Young had no business being on the cover in 08, but if you ignore the TD-INT ratio (9-17 in 2007, vs. 12-13 in 2006) he actually had a better year than he did the year before in pretty much every other category (including record).
Drew Brees posted an 11-5 record, and at the time posted career 2nd bests in Passing TDs, Yards, and Completion percentage and set the career high for completions (which he has since broken). The only negative part about that season was the number of INTs he threw (22).
Peyton Hillis had no business being on the cover of Madden 12, he had one good year under his belt, and won because he was a commodity (a white running back). Aaron Rodgers should have been on the cover but twice had to face white running backs who had no business being in the competition (He barely edged out Danny Woodhead, and then got killed by Peyton Hillis). Peyton Hillis, might have done better if he focused on playing the damn game rather than holding out for money after only 1 season of production, but even then it would have been hard to match the numbers he put up the year before because he was in Cleveland, and he wasn't an elite RB.
And then Calvin Johnson broke the record for Receiving yards for a season, falling just short of the 2000 yard mark he boldly stated he would surpass. Yeah the Lions had a bad season record wise, but I'll chalk that up to them being the Lions long before I'll even consider some "curse".
The curse doesn't exist, this is simply what happens when you play in the NFL (where careers average a length of 3-4 years), the fact that multiple times the curse has been broken by stellar performances (and/or zero injuries), and yet people keep getting hurt should tell you its a product of the brutality of the game not the magic of a cover.